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Background: Lansoprazole is a potent proton-pump inhibitor (PPI) of parietal cells, which reduces the secretion of gastric acid. Although human gastric lipase (HGL) is produced only by the chief cells of the stomach, the possibility that interactions may occur between lansoprazole and HGL has never been addressed so far in humans. The aim of this study was therefore to quantify the effects of lansoprazole on HGL secretion and intragastric lipolysis during the ingestion of test meals by healthy human volunteers. Methods: Six healthy volunteers were intubated twice with a gastric and a duodenal tube, before ingesting a standard liquid test meal alone (–PPI experiments) and after 7 days of lansoprazole treatment (+PPI experiments). The HGL concentration was assessed in gastric and duodenal samples by measuring the lipase activity using a pH-stat, and the lipolysis products were quantified by performing thin layer chromatography. The level of intragastric lipolysis was defined as the percentage acyl chains released from the meal triglycerides. The pyloric outputs of HGL and lipolysis products were calculated, based on the use of a non-absorbable marker added to the meal. Results: The pH of the gastric contents was significantly higher in the +PPI experiments than in the –PPI experiments (p < 0.05), since mean values of 4.3 ± 2.5 and 2.2 ± 1.6, respectively, were recorded at the end of the gastric emptying of the meal. The HGL concentrations recorded during the meal were found to be higher in the experiments with lansoprazole (p < 0.05) than in those without lansopra- zole, but the HGL secretion levels (–PPI: 15.4 ± 8.0 mg; +PPI: 19.0 ± 7.4 mg) and the intragastric lipolysis (–PPI: 24.0 ± 8.0%; +PPI: 23.6 ± 6.8%) were not significantly affected by lansoprazole (p > 0.05 in both cases). Conclusion: Lansoprazole affected neither the HGL secretion nor the intragastric lipolysis levels, although an increase was observed in the intragastric pH at the end of the gastric emptying of the meal. The HGL concentration increased, however, due to the decrease in the acid secretion process, resulting in less diluted gastric contents.